ublic class ArrayList<E> extends AbstractList<E>

        implements List<E>, RandomAccess, Cloneable, java.io.Serializable

{

    private static final long serialVersionUID = 8683452581122892189L;

    /**

     * Default initial capacity.

     */

    private static final int DEFAULT_CAPACITY = 10;

    /**

     * Shared empty array instance used for empty instances.

     */

    private static final Object[] EMPTY_ELEMENTDATA = {};

    /**

     * The array buffer into which the elements of the ArrayList are stored.

     * The capacity of the ArrayList is the length of this array buffer. Any

     * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to

     * DEFAULT_CAPACITY when the first element is added.

     */

    private transient Object[] elementData;

    /**

     * The size of the ArrayList (the number of elements it contains).

     *

     * @serial

     */

    private int size;

}

/**

     * Appends the specified element to the end of this list.

     *

     * @param e element to be appended to this list

     * @return <tt>true</tt> (as specified by {@link Collection#add})

     */

    public boolean add(E e) {

        ensureCapacityInternal(size + 1);  // Increments modCount!!

        elementData[size++] = e;

        return true;

    }

/**

* Increases the capacity of this <tt>ArrayList</tt> instance, if

* necessary, to ensure that it can hold at least the number of elements

* specified by the minimum capacity argument.

*

* @param   minCapacity   the desired minimum capacity

*/

public void ensureCapacity(int minCapacity) {

int minExpand = (elementData != EMPTY_ELEMENTDATA)

// any size if real element table

? 0

// larger than default for empty table. It's already supposed to be

// at default size.

: DEFAULT_CAPACITY;

if (minCapacity > minExpand) {

ensureExplicitCapacity(minCapacity);

}

}

private void ensureCapacityInternal(int minCapacity) {

if (elementData == EMPTY_ELEMENTDATA) {

minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);

}

ensureExplicitCapacity(minCapacity);

}

private void ensureExplicitCapacity(int minCapacity) {

modCount++;

// overflow-conscious code

if (minCapacity - elementData.length > 0)

grow(minCapacity);

}

/**

* The maximum size of array to allocate.

* Some VMs reserve some header words in an array.

* Attempts to allocate larger arrays may result in

* OutOfMemoryError: Requested array size exceeds VM limit

*/

private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

/**

* Increases the capacity to ensure that it can hold at least the

* number of elements specified by the minimum capacity argument.

*

* @param minCapacity the desired minimum capacity

*/

private void grow(int minCapacity) {

// overflow-conscious code

int oldCapacity = elementData.length;

int newCapacity = oldCapacity + (oldCapacity >> 1);

if (newCapacity - minCapacity < 0)

newCapacity = minCapacity;

if (newCapacity - MAX_ARRAY_SIZE > 0)

newCapacity = hugeCapacity(minCapacity);

// minCapacity is usually close to size, so this is a win:

elementData = Arrays.copyOf(elementData, newCapacity);

}

private static int hugeCapacity(int minCapacity) {

if (minCapacity < 0) // overflow

throw new OutOfMemoryError();

return (minCapacity > MAX_ARRAY_SIZE) ?

Integer.MAX_VALUE :

MAX_ARRAY_SIZE;

}

/**

     * Removes the element at the specified position in this list.

     * Shifts any subsequent elements to the left (subtracts one from their

     * indices).

     *

     * @param index the index of the element to be removed

     * @return the element that was removed from the list

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    public E remove(int index) {

        rangeCheck(index);

        modCount++;

        E oldValue = elementData(index);

        int numMoved = size - index - 1;

        if (numMoved > 0)

            System.arraycopy(elementData, index+1, elementData, index,

                             numMoved);

        elementData[--size] = null; // clear to let GC do its work

        return oldValue;

    }

　　

/**

* Removes the first occurrence of the specified element from this list,

* if it is present.  If the list does not contain the element, it is

* unchanged.  More formally, removes the element with the lowest index

* <tt>i</tt> such that

* <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>

* (if such an element exists).  Returns <tt>true</tt> if this list

* contained the specified element (or equivalently, if this list

* changed as a result of the call).

*

* @param o element to be removed from this list, if present

* @return <tt>true</tt> if this list contained the specified element

*/

public boolean remove(Object o) {

if (o == null) {

for (int index = 0; index < size; index++)

if (elementData[index] == null) {

fastRemove(index);

return true;

}

} else {

for (int index = 0; index < size; index++)

if (o.equals(elementData[index])) {

fastRemove(index);

return true;

}

}

return false;

}

/*

* Private remove method that skips bounds checking and does not

* return the value removed.

*/

private void fastRemove(int index) {

modCount++;

int numMoved = size - index - 1;

if (numMoved > 0)

System.arraycopy(elementData, index+1, elementData, index,

numMoved);

elementData[--size] = null; // clear to let GC do its work

}